1. Field of the Invention
This invention relates to gas turbine engines and more specifically to apparatus for premixing gaseous or vaporized fuel with air upstream of the combustion chamber.
2. Description of the Prior Art
Increasingly restrictive environmental pollution standards and dramatically increased fuel costs are causing engine manufacturers to devote substantial financial and valued personnel resources to the search for more efficient and cleaner combustion systems. Although much art now exists in the field, the opportunity for technical improvement remains.
Combustion apparatus is classifiable into two principal categories based upon the type of fuel delivery technique employed: pressure atomizing systems and premixing systems. Each type of system has inherent advantages over the other system and each system has become, therefore, of cyclical interest to the industry as engine performance and combustion efficiency requirements have varied through the years. The systems embodying premixing techniques, have high combustion efficiency characteristics and produce low levels of noxious pollutants. Traditional apparatus implementing premixing theory have, however, failed to achieve the full potential of premixing techniques for reducing noxious contaminants in the effluent from the combustion chamber while meeting the rigorous performance and stability characteristics required of turbine engines. Specifically, the stable operation of premixing systems at low power has been one nagging problem and a widespread deterrent to the fully successful implementation of these systems in engines.
The search for systems capable of stable operation at low power has forced engine manufacturers to staged combustion wherein fuel is flowable through a primary system at low power and jointly through primary and secondary systems at high power. Although staged combustion in premixing systems is known, the totally successful manifestation of this technique in physical hardware for low BTU fuels has heretofore eluded scientists and engineers working in the field.